Some conventionally known coating-type magnetic recording media have a magnetic layer that is formed by applying, onto a nonmagnetic support, a magnetic coating material including a magnetic powder, a binder, and an organic solvent, and then drying the coating material. Such coating-type magnetic recording media are widely used as high-density recording media such as backup data cartridges.
In recent years, magnetic powders for use in magnetic layers have been made finer for recording media with higher recording density. However, magnetic powders with further reduced particle sizes can be affected by external heat in the environment where magnetic tapes are used, so that the influence of what is called thermal agitation of magnetization can be significant to cause a phenomenon in which the recorded magnetization disappears. To avoid the influence of the thermal agitation of magnetization, it is necessary to increase the magnetic anisotropy or coercivity of magnetic powders.
However, an increase in coercivity can make it difficult for recording heads to cause magnetic reversal, in other words, make it difficult to record information signals. In addition, magnetic powders with further reduced particle sizes may have lower saturation magnetization σs, which, together with a decrease in output due to high-density recording, may cause significant degradation of signal-to-noise ratio or carrier-to-noise ratio (hereinafter referred to as “CNR”).
To solve these problems, it is proposed that a soft magnetic coating film with a high saturation magnetization σs be formed around hard magnetic particles so that each hard magnetic particle as a core portion can be exchange-coupled with the soft magnetic coating film as a shell portion, which makes it possible to control the coercivity to a value suitable for recording and to increase the saturation magnetization σs while high thermal stability is maintained (see Patent Documents 1 to 3).